A plurality of cloud service providers provide storage services for a function of storing or reconstructing large capacity data and, for example, provide a function of manually or automatically (sync) uploading personal contents (for example, images, documents, applications, and the like) of a terminal to a cloud server through a link with the user terminal.
In general, the personal contents uploaded to the cloud server may be stored in the terminal and the cloud server in a raw data type to which a separate encryption scheme has not been applied, such that personal information may be leaked from the personal contents through cloud service hacking or by a cloud service provider. For example, a personal image file, which is stored in the cloud server, may be exposed to the outside through cloud service hacking, which causes a problem.
The conventional art is directed to a method of encrypting an original image in a client terminal and then uploading the encrypted original image to the cloud server in order to protect contents to be stored in the cloud server. When the encrypted original image is uploaded to the cloud server, the cloud server may generate a thumbnail image based on the uploaded encrypted original image.
However, when the thumbnail image generated by the cloud server is downloaded to the client terminal, the client terminal may decrypt the downloaded thumbnail image since information on the original image is lost during the generation of the thumbnail image by the cloud server.
Accordingly, in order to display the thumbnail image of the encrypted original image, the client terminal should perform a process of downloading the whole encrypted original image from the cloud server, decrypting the downloaded encrypted original image, and then generating the thumbnail image, but such a process uses unnecessary network packets and requires an overlapping thumbnail image generation process.